University of New South Wales School of Photovoltaic & Renewable Energy Engineering SOLA5017 GSOE9017: Managing Energy Efficiency Due Date: 11:59 pm Friday 2nd June, 2017 Week 13 Hand in SOFT COPY only via Moodle (pdf) Include a coversheet https://www.engineering.unsw.edu.au/energy-engineering/sites/photo/files/u12/forms/individualcoversheet.pdf Assignment 2 Answer all THREE questions. Question 1: PC VS LAPTOP 1. A University is costing the replacement of 275 of the libraries computers. The options are: Base Scenario (business as usual) - OptiPlex™ GX280 Mini Tower and 1704FPVt Screen (Capital Cost $1200 per computer, Data Sheet provided) Option 1 (saving option if cost effective)- Precision M20 laptop (Capital Cost $1400 per computer, Data Sheet provided). Information: Use the following energy tariffs to calculate the energy costs of the systems: Off peak power: $0.12 per kWh. Shoulder power: $0.21 per kWh. Peak power: $0.29 per kWh. The appropriate times for these tariffs (for both weekdays and weekends) are given in Appendix A at the end of this document. NOTE: For your answers, outline your method of calculation and where appropriate present your answers in a Table. Questions a. Calculate the total expected yearly energy usage (kWh) and energy cost ($) of each option based on the following usage pattern. The computers will be operating 350 days per year (250 weekdays and 100 weekend days). See provided data sheets (see Additional Information.pdf) for energy usage in different modes of operation.Mode of Operation Hours Operating On (Maximum) 10am – 2pm (4 hrs per day) Standby (Low Power Sleep Mode) 8am – 10am and 2pm – 7pm (7 hrs per day) Off 7pm – 8am (13 hrs per day) b. Calculate the NPV for Option 1 compared to the base case. Assume the computers will last for 6 years. Apply a discount rate of 5%. c. Which is the best option financially? d. Which is the best option energy wise? e. The electricity prices are expected to rise by 2.5% per year for the next 5 years. Recalculate the NPV of Option 1 compared to the base case, on this basis. f. Write a brief explanation of your findings (1 paragraph) and your recommendation to the University. Question 2: EXHAUST SYSTEM You are required to look at the energy needed for ventilation of a carpark space in an existing building. The exhaust duct will rise up through the building, into the plantroom on the roof of the building where the fan will be located. The fan will then discharge the air. The effective length of the duct is 85 meters from intake to discharge (i.e. this includes pressure drop due to grilles, bends and dampers). You need to consider the pressure the fan needs to produce in order to: i) impart to the air the kinetic energy required at the output of the duct and ii) overcome frictional losses in the duct (major and minor losses). For the purpose of this question, the pressure drop due to frictional losses in the duct (major and minor losses) is given by: pressure loss per metre (Pa/m) x effective length of the duct (m). There are three alternative duct sizes for the application to be considered: Duct 1 - 600 mm x 600 mm which operates at 3 Pa/m. Duct 2 - 750 mm x 750 mm which operates at 1 Pa/m. Duct 3 - 1000 mm x 1000 mm which operates at 0.25 Pa/m The pressure drops per metre are for the required volume flow rate of 5000 l/s. Average velocities in the duct can be calculated by considering the volume flow rate and cross sectional area of the ducts. You may assume the air density is 1.20 kg/m3.For each duct size you need to select a single fan that uses the least energy but will provide the air flow rate and pressure and requirements of the system. The performance curves of SIX fans are provided (see Additional Information.pdf). Assume that the electrical power drawn by the fan is the same for any flow rate and pressure the fan is capable of delivering. Therefore, the electrical power consumed by a fan is given in the section labelled “Motor Data”: Rated (kW). For example the fan: LE80JL25P-4GSF, has an electrical motor with a rated power of 3 kW. The costs of the fans are given below as a function of their rated power. Also shown in the table is the manufacturer’s recommended maximum pressure for the fan Power (kW) 0.75 1.1 2.2 3 4 5.5 Cost ($) 1645 1725 1845 1926 2020 2175 Max. Press. (Pa) 80 100 175 300 500 800 Assume that the cost of mounting and installing the different size fans is the same for all fans at $5,650. The ductwork costs $64 per square metre, fabricated and installed. This area is related to the surface area of the metal used to construct the ducts (NOT the cross sectional area of the duct for air-flow). That is you will need to use the effective air path length to calculate the surface area of the duct. This includes an allowance for all the duct and associated items including bends, grilles and dampers. The fans will operate from 7am to 7pm, 12 hours per day, 7 days per week, 48 weeks per year. The electricity costs are: Off peak power: $0.10 per kWh. Shoulder power: $0.19 per kWh. Peak power: $0.48 per kWh. The appropriate times for these tariffs (for both weekdays and weekends) are given in Appendix A at the end of this document. Questions: a. Present a table which shows for each duct: i) the average velocity of the air in the duct to meet the required volume flow rate, ii) the pressure a fan needs to produce to overcome the frictional losses in the duct, iii) the pressure a fan needs to produce to supply the air with kinetic energy, iv) the total pressure required, v) which fans are suitable for each duct (specify fans by their power in kW). Choose ONE fan per duct (select the fan that you believe will have the lowest energy usage). vi) the maximum fan motor power to air flow rate ratio. (units W/(l/s)). vii) whether the above metric meets the National Construction Code (NCC) for a carpark exhaust system in a high rise residential building? Please state the value required by the NCC for a carpark exhaust system without filters. (HINT – the NCC is NO longer available via UNSW library. Instead it can be downloaded off the web page of the Australian Building Code Board).b. For each duct and fan combination selected in part (a), present in a table the electricity cost for: i) a weekday, ii) a weekend day, ii) a week, iv) a year & v) 10 years. c. Assuming the life of the equipment is 15 years; calculate the NPV of each solution in comparison to the NPV for the smallest duct. Apply a discount rate of 6% per year. Assume that the price of power will be inflated by 3% each year. d. Which option is the most cost effective combination for the application? Question 3: COGENERATION You represent a consultant who has been contracted to evaluate the feasibility of a cogeneration plant for an aquatic centre in New South Wales. You need to evaluate the viability of supplying and installing the cogeneration plant. Your task is to size the cogeneration plant on the current electrical demand as the facility has had a recent upgrade and is not likely to increase its electrical demand in the foreseeable future. There are three cogeneration units being considered, which have maximum electrical outputs of 1200, 1600 and 2000 kW . Technical details of these units can be found in the attached document (see Additional Information.pdf). You should compare the results for all three units and propose the best solution for the facility and justify your choice in a single page proposal. Details The aquatic centre has two pools with a total volume of 1.7 million litres. The facility is open 365 days per year. The pool is currently heated by two natural gas fired boilers to a water temperature of 28oC. Electrical load data for the aquatic centre is provided in the Excel file (Asst2Q3.xls). The data is for a typical day’s operation. Assume that the data is typical for a day of operation for both weekdays and weekends throughout the year. The data is given in 5 minute intervals in kilowatts (kW). Each cogeneration unit has THREE heat exchange opportunities with i) an exhaust gas heat exchanger, ii) a jacket water heat exchanger and iii) an intercooler water heat exchanger. This heat can be transferred into the pool with an efficiency of 75%. Each of these circuits will require a secondary water pump to be operating. The facility currently pays the following rates for its electricity: Off peak power: $0.12 per kWh. Shoulder power: $0.21 per kWh. Peak power: $0.29 per kWh.The appropriate times for these tariffs (for both weekdays and weekends) are given in the Appendix at the end of this document. The cogeneration plant has a projected working life of 100,000 hrs. Maintenance costs for the cogeneration plant are $0.03 per kWh (electrical) at full electrical output. For simplicity only consider running the cogeneration systems at full capacity and only when the electrical demand of the aquatic centre exceeds or equals the electrical output of the cogeneration system. Also the cogeneration plant cannot continue to run if there is insufficient heat demand. This may occur for example in summer when there is less heat demand. THE EXISTING POOL HEATING SYSTEM Gas consumption data is provided in the Excel file (Asst2Q3.xls). The data is for the past years operation. Accept this data as the typical annual gas consumption. The facility pays $12.00 per gigajoule. The pool heating system (two gas fired boilers) are the only gas appliances on the site. The boilers have a thermal efficiency of 80%. Questions a. Establish how much electricity the aquatic centre consumes on the typical day. Express your answer in kWh. b. Produce a graph showing the kWh consumption profile for the typical day at five minute intervals. Label your graph axes appropriately. c. Establish the current cost of the electrical power supplied to the facility from the grid. Calculate the cost per weekday, the cost per weekend-day, the cost per week (7 days) and the cost per year (52 weeks) for electricity. d. Establish the current total gas consumption for the year and its cost. Gas consumption for each month of the year is given in the excel file (Asst2Q3.xls). e. Consider the three alternative cogeneration units. From their electrical output, subtract the power that must be supplied to the pumps which operate when the cogeneration systems are running. This will produce the net electrical output which you should use to select the most suitable unit. f. For each cogeneration unit - how many hours per day should they operate and at what time? Consider the following issues:  Are there months of the year when any of the cogeneration plants could be running (due to electrical demand) but are unable to as there is limited demand for heat? When optimising your schedule you should also consider the economics of your proposed schedules. For example one aspect that you need to consider when scheduling a cogeneration system is the economics of running the cogeneration system (and the cost of gas for water heating and additional electricity) vs purchasing electrical power and gas for heating only. g. Calculate the yearly energy costs as well as maintenance costs for the cogeneration systems to run the aquatic centre for each of the three cogeneration plants using the schedules you believe are optimum in each case. (Include the cost of the gas for both the cogeneration plant as well as for operating the gas boilers if needed, maintenance costs for the cogeneration plant and the cost of the additional electricity that must be purchased from the grid). h. Calculate the total energy costs per year to run the aquatic centre for the business as usual case. Report the electricity and gas costs as well as the total cost. i. Compare your yearly energy costs for each cogeneration unit to the “business as usual” case. Calculate the yearly savings (if any!). j. Calculate the simple payback period for each cogeneration unit. k. Develop a half-page page proposal for the facilities manager describing the advantages you see for the best solution for the facility. APPENDIX 1: FOR ALL QUESTIONS: The appropriate times for the tariffs (for both weekdays and weekends) are: Peak 2 pm to 8 pm on working weekdays Shoulder 7 am to 2 pm and 8 pm to 10 pm on working weekdays 7 am to 10 pm on weekends and public holidays Off Peak All other times